There are a few other skins that are available that are not currently listed on the website.

There is the Dark Mode skin for the steam community and store pages here AikoMidori/steam-dark-mode

There is a fork of that skin that has a little more features (though AikoMidori is working on a big update to the original version) here, which I am currently using myself BallOpener/steam-dark-mode/blob/beta2/css/webkit.css

RoseTheFlower has a friends skin (and wip library and I think client skin) here RoseTheFlower/newsteamchat

The link to download the AikoMidori/SteamSkins repo could be replaced with a direct link to the download for the individual folders.

e.g. :

Metro - https://download-directory.github.io/?url=https://github.com/AikoMidori/SteamSkins/tree/main/Metro/

Fluent - https://download-directory.github.io/?url=https://github.com/AikoMidori/SteamSkins/tree/main/Fluent/

and then the Metro-JS version could also be directly linked:

Metro-JS - https://download-directory.github.io/?url=https://github.com/AikoMidori/SteamSkins/tree/main/Metro/Metro-JS/

Though the Metro-JS link does not work perfectly as the resulting zip still has Metro as its root folder with Metro-JS being a subfolder. I opened an issue on the download-directory github repo about this download-directory/download-directory.github.io#98

https://github.com/tkashkin/Adwaita-for-Steam
Mostly targeted towards Linux users as it tries to mimic the GNOME UI but it works on Windows too, looks like a nice skin :)